Scale‐Dependent Estimability of Turbulent Flux in the Unstable Surface Layer for Land Surface Modeling

Author:

Liu Shaofeng12ORCID,Zeng Xubin3ORCID,Dai Yongjiu12ORCID,Yuan Hua12ORCID,Wei Nan12ORCID,Wei Zhongwang12ORCID,Lu Xingjie12ORCID,Zhang Shupeng12ORCID,Li Xian‐Xiang12ORCID

Affiliation:

1. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) School of Atmospheric Sciences Sun Yat‐sen University Zhuhai China

2. Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies Sun Yat‐sen University Zhuhai China

3. Department of Hydrology and Atmospheric Sciences The University of Arizona Tucson AZ USA

Abstract

AbstractSurface flux estimation is essential to land surface modeling in earth system models. In practice, parameterizations of surface turbulent fluxes are almost all based on the similarity theory. That is, the grid or subgrid mean surface‐layer flow is assumed at equilibrium with the underlying earth surface, and therefore some empirical relations can be used to estimate surface fluxes. In this paper, scale‐dependent estimability of turbulent flux in the unstable surface layer is systematically investigated based on high‐resolution large‐eddy simulation data over a flat and homogeneous domain, representing a typical land surface modeling grid. It is found that turbulent flow in the unstable surface layer inherently fluctuates over a wide range of scales. This kind of fluctuation affects the steady‐state relations between mean atmospheric quantities and underlying earth surface, and hence affects the estimability of surface fluxes. Sensitivity tests show that the relative root mean square error of the estimated surface friction velocity for a subdomain generally increases as the subdomain becomes smaller. The error can be as high as 35% as the subdomain size decreases to the order of the surface layer height. To achieve an error of 10% for all cases, the subdomain size should be at least on the order of the boundary layer height. These findings imply that estimability‐based strategies may be needed for representing subgrid heterogeneity for surface flux estimation in land surface modeling.

Funder

National Natural Science Foundation of China

Publisher

American Geophysical Union (AGU)

Subject

General Earth and Planetary Sciences,Environmental Chemistry,Global and Planetary Change

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